The major objective of the proposed research is to understand the molecular biology of regulation of muscle contraction by troponin and calcium. Experiments are outlined to study the surface of native troponin from rabbit skeletal muscle, isolated and in combination with actin and tropomyosin, using a competitive labeling procedure. The relative reactivity of the epsilon-amino groups of lysine with acetic anhydride will be related to the amino acid sequence of each troponin component. Determination of which residues are "inaccessible" and which are freely "accessible" should elucidate the areas of each protein involved in conformational changes and interaction with the other proteins in the thin filament. Another area of research is regulation of the contractile process in human blood platelets. Tropomyosin will be isolated and the amount of this thin filament regulatory protein will be quantitated using radioimmune assay. The possible presence of troponin-like regulatory proteins will be investigated. The third part of the proposal is the investigation of the interaction between actin and pancreatic DNase I. DNase I depolymerized a filamentous actin to form a 1:1 complex with monomeric actin. This interaction will be investigated using actin that has been labeled with fluorescent probes in order to learn more about the structure of actin when it binds to DNase I as well as other contractile proteins.